This invention relates to medical, diagnostic ultrasound transducer array configurations and switching schemes, and more particularly to a switching system and method for forming ultrasound beam lines.
Medical diagnostic ultrasound systems are commonly used to generate two-dimensional diagnostic images of internal features within a patient's body. To do so, a sonographer positions an ultrasound transducer probe adjacent to a patient's target area. The probe is a non-intrusive device including an array of acoustic transducer elements. The transducer elements emit ultrasonic energy at a frequency on the order of 2.0 MHz to 10 MHz. The transmitted ultrasound energy propagates into the patient where it is in part absorbed, dispersed, refracted, and reflected by internal structures. Reflected ultrasound energy is received back at the transducer probe where it is converted back into electronic signals. Body tissues, for example, appear as discontinuities or impedance changes in the converted electronic signals.
Converted electronic signal samples undergo beamforming to correlate the samples in time and space to a patient's target area. Exemplary beamforming parameters for controlling the imaging process include focus, steering, apodization and aperture. Focus is a time delay profile of active transducer elements. Steering is the control of focus depth points along azimuth and/or elevation axes of a transducer probe scan. Apodization is a voltage weighting profile of active transducer elements. Aperture is the control of the number of transducer elements which are active along azimuth or elevation axes of the transducer probe for a given scan. Beamformed data is processed to analyze echo, doppler, and flow information and obtain a cross-sectional image of the patient's targeted anatomy (e.g., tissue, flow, doppler).
A conventional image is a brightness image (i.e., referred to as a `B-mode image`) in which component pixels are brightened in proportion to a corresponding echo sample strength. The B-mode image represents a cross section of the patient target area through a transducer's scanning plane (e.g., xz-plane). Typically the B-mode image is a gray scale image in which the range of lighter to darker gray-scale shades correspond to decreasing brightness or echo strength. The typical ultrasound B-mode image is formed by a linear scan or sector scan of the patient's target area by the transducer probe.
Among known transducer array configurations are linear 1-dimensional (`1-D`) arrays and non-linear multi-dimensional arrays. A 1-D array includes a single row of transducer elements. A multi-dimensional array includes multiple rows of transducer elements along at least a portion of the array. A linear array having 64 transducer elements has 64 channels to control. A multi-dimensional array having n rows of 64 elements per row has as many as 64.times.n channels to control.
FIG. 1 depicts a conventional filled 2-D ultrasound transducer array 10. The array 10 includes a plurality of rows 12. Each row 12 includes a plurality of transducer elements 14. Each element 14 is formed of a piezoelectric material. The rows 12 extend along an azimuthal ("x") direction in parallel with one another. The rows 12 are spaced in an orthogonal elevation ("y") direction. For the conventional 2-D array each element 14 is independently controlled to perform either one or both of transmitting and receiving ultrasound signals. For a 2-D array 10 having 5 rows 12 and 64 transducer elements 14 per row, there are 64.times.5 channels to control. The transducer 10 emits and receives ultrasound signals to define an xz image plane 16.
FIG. 2 depicts a conventional 1.5-D ultrasound transducer array 20. The array 20 includes a plurality of rows 22 of transducer elements 24. Each row 22 extends along an azimuthal ("x") direction. The rows 22 are parallel and spaced orthogonally in an elevation ("y") direction. In contrast to the 2-D array, however, the transducer elements 24 are not independently controlled. For a conventional 1.5-D array an element 24a in one row 22-B1 is coupled to a corresponding element 24a in a symmetrical row 22-B2. A center row 22-A defines an axis of symmetry. Corresponding elements in the first row on each side of the center row (i.e., 22-B1 and 22-B2) are electronically connected. Similarly, corresponding elements in the second row, if any, on each side of the center row (i.e., 22-C1 and 22-C2) are electronically connected. Thus, elements 24a of rows 22-B1 and 22-B2 are connected, elements 24b of rows 22-B1 and 22-B2 are separately connected, elements 24a of rows 22-C1 and 22-C2 are separately connected, and elements 24b of rows 22-C1 and 22-C2 are separately connected. For a 1.5-D array 20 having five rows, 22-A, 22-B1, 22-B2, 22-C1 and 22-C2, in which each row has 64 elements, there are 64.times.3 separate channels to control. The transducer 20 emits and receives ultrasound signals to define an xz image plane 26.
To develop an image of a scanned image plane of a patient, the transducer elements are controlled to define aperture, focus, steering and apodization profiles. For a 1.5-D array beamforming controls along the elevation (y-axis) are limited. Specifically, steering of the beam is controlled along the azimuth, but not the elevation. Focus along the elevation is symmetrical. Apodization profiles along the elevation are symmetrical. This invention is directed toward a switching scheme for a static scanhead 1.5-D transducer array which improves image resolution of a displayed image plane.